[104] [cap.20] However, besides what has been here said, any one may use this argument also in corroboration of his opinion, which will certainly convince all those who are not determined to be obstinate beyond all bounds; of those things which in pairs are exactly contrary to one another it is impossible that one thing should be, and that the other should not be; for since there is white it follows as a matter of absolute necessity that there must also be black, and since there is a great there must likewise be a little; since there is an odd there must inevitably be an even; since there is a sweet there must be a bitter; since there is day there must be night; and so on in an infinite number of similar cases; but if a [29] conflagration should take place, then something would ensue which is impossible; for then, of things in a pair, the one will happen and the other will not.